The present device may be used in separating any fluid having at least two phases of differing densities, such as plasma, cellular material, or platelets. However, the following description is directed to the collection and separation of whole human blood for which the device is especially adapted.
It is an established practice to centrifuge blood to effect a separation into its two major components or phases, namely, a light serum portion and a heavier clot portion consisting mainly of red blood cells. Such separation of whole blood into its two principal phases has greatly facilitated physical and chemical analyses of blood.
However, simple centrifugation of whole blood does not necessarily effect an ideal separation for analytical purposes. It is known, for example, that once blood phases are separated, if the lighter phase is not removed within a relatively short time, interaction occurs between the separated phases and inaccurate test results are apt to be obtained. Moreover, clinics and hospitals are meeting increasing demands on their services for more routine as well as specialized diagnostic tests of blood.
In an attempt to overcome the problems associated with simple centrifugation, it has been proposed to use various materials or compositions having a specific gravity between those of the serum and clot portions to assist in separating such portions. These compositions have physical and chemical properties which, in the presence of whole blood, permit the composition to be centrifuged to a position intermediate that of the serum and clot portions and thereby form a sealing barrier or partition between the two portions. For the composition to function as a barrier, it must be viscous at rest, like petroleum jelly, and yet flow freely under centrifugal forces to a proper position between the two blood phases.
For example, the earliest attempt known to applicant to provide a sealant material comprises a mixture of a silicone fluid, particularly polysiloxanes, and silica as illustrated by U.S. Pat. No. 3,780,935 to Lukacs et al, U.S. Pat. No. 3,852,194 to Zine, and U.S. Pat. No. 4,043,928 to Lukacs et al. U.S. Pat. No. 3,977,982 to Hertl, U.S. Pat. No. 4,083,748 to Zine, and U.S. Pat. No. 4,043,784 to Zine also describe compositions for this purpose comprising a silicone fluid and silica in which the silicone fluid may be polysiloxanepolyoxyalkyl copolymers.
U.S. Pat. No. 4,021,340 to Zine suggests using, in lieu of a silicone fluid-silica system, one comprising a liquid polybutene having dispersed therein a siliceous filler. U.S. Pat. No. 4,055,501 to Cornell describes a three component system for a barrier for separating blood phases comprising a hydrocarbon polymer, a hydrophobic silica powder, and a hydrophilic silica powder. The hydrocarbon polymer may be liquid polybutene, liquid butyl rubber, or liquid polybutadiene.
While the use of thixotropic sealing barriers between separated serum and clot phases has improved the technique of sampling and analyzing whole blood, this use has not removed the danger of infecting a patient due to backflow attending the sampling of his blood. For example, in the usual sampling procedure, the practice is to withdraw blood from a vein of a patient through a tubular needle and into a specimen tube or other collection device which may be partially evacuated to assist in the blood flow. Unfortunately, the collection device often is not sterile. The backflow of blood to a patient from a collection or specimen tube, as when disconnecting the sampling apparatus, can contaminate the patient due to the carry-back of bacteria originally present within the collecting device. For example, the spread of hepatitus can occur in this manner.
Sterilization as by gamma radiation of commercial gel-containing blood collecting devices has not previously been thought to be possible, because the gels were not expected to withstand the radiation. Properties of the gels are normally altered by radiation, such that the gel can no longer function as desired. For example, commercially available silicone-based serum separator gels, particularly the polysiloxanes, set up under sterilizing radiation. Their viscosities increase greatly and they become non-flowable and rubbery.